Fig. 4: Schematic illustration of the fate of carbonates in the oceanic crust (dark blue) subducted to the lower mantle.
From: Reversal of carbonate-silicate cation exchange in cold slabs in Earth’s lower mantle
Through subduction, the carbonates may undergo melting (red arrow), redox freezing with metallic iron (purple arrow), decarbonation reaction with free silica (blue arrow), and exchange reaction with lower-mantle silicates (green arrow). Based on the observation of reversal of the carbonate–silicate cation exchange reaction at conditions relevant to cold subducted slabs at mid-lower-mantle depths, CaCO3 is the potential stable phase that hosts oxidized carbon in the lowermost mantle.
